Stockholders' Equity - Reclassifications from accumulated other comprehensive income (loss) and included in net income (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Reclassifications from accumulated other comprehensive income (loss)
Reclassifications included in net income:
Pre-tax	$ (1,103)	$ (1,777)
Tax (expense) benefit	465	619
Net of tax	(638)	(1,158)
Realized gain (loss) on sale of sponsored investment securities | Investment and other income (loss) | Reclassifications from accumulated other comprehensive income (loss)
Reclassifications included in net income:
Pre-tax	148	(81)
Tax (expense) benefit	(56)	30
Net of tax	92	(51)
Change in valuation allowance for unrealized gains (losses) on investment securities
Reclassifications included in net income:
Net of tax	56	(30)
Change in valuation allowance for unrealized gains (losses) on investment securities | Provision for income taxes | Reclassifications from accumulated other comprehensive income (loss)
Reclassifications included in net income:
Tax (expense) benefit	56	(30)
Net of tax	56	(30)
Pension and postretirement benefits
Reclassifications included in net income:
Net of tax	(786)	(1,077)
Pension and postretirement benefits | Underwriting and distribution expense and Compensation and related costs | Reclassifications from accumulated other comprehensive income (loss)
Reclassifications included in net income:
Pre-tax	(1,251)	(1,696)
Tax (expense) benefit	465	619
Net of tax	$ (786)	$ (1,077)